Manufacturing low-spore-count skim milk powders by combining optimized raw milk holding conditions and hydrodynamic cavitation

Document Type


Publication Date



2019 American Dairy Science Association Annual Meeting: Cincinnati, Ohio


American Dairy Science Association


Journal of Dairy Science










cavitation, spore, powder


The presence of high numbers of Bacillus spores in skim milk powder limits its application for creating UHT products. The dairy industry has been emphasizing on developing strategies for reducing sporeformers and spores in skim milk powder. Previous studies conducted in our 10 J. Dairy Sci. Vol. 102, Suppl. 1 lab showed that it is possible to produce lower spore count skim milk powder, either by optimizing raw milk holding conditions or by using hydrodynamic cavitation as a process intervention. It was hypothesized that by combining the 2 processes it may be possible to further lower the sporeformers and spore counts in the final product. Pilot-scale challenge studies were conducted by spiking raw skim milk with approx. 4.0 log cfu/mL sporeformers and 2.0 log cfu/mL spores of Bacillus licheniformis. The inoculated raw skim milk was divided in to 3 parts and exposed to 3 treatment (T1, T2 and control) for keeping the spore and sporeformer populations low in raw milk, before manufacturing skim milk powder. Powder prepared using treatment 1 (T1) includes raw milk holding at 4°C for 24 h, treatment 2 (T2) includes holding at 4°C for 24 h combined with 2 pass hydrodynamic cavitation, whereas, control includes holding raw spiked skim milk at 10°C for 4 h and then at 7°C for up to 72 h (PMO based conditions). Spiked raw milk samples from all 3 treatments were HTST pasteurized (73°C for 15 s), evaporated, and dried (outlet and inlet temperature of 200 and 95°C) to obtain skim milk powders. Spore and sporeformer counts of samples from 3 treatments were statistically compared after initial treatments (T1, T2, and control), pasteurization, evaporation, and drying steps. Final spore and sporeformer counts from powder prepared using T1 (0.58 ± 0.04, 1.82 ± 0.05 log cfu/g), T2 (0.33 ± 0.27, 1.49 ± 0.07 log cfu/g) and control (2.74 ± 0.03 and 1.03 ± 0.06 log cfu/g) were significantly different (P < 0.05) with respect to each other. Our results demonstrate that combining cavitation with optimized raw milk holding conditions (treatment T2) produces skim milk powder with least sporeformers and spore counts.